The present invention relates to a glazed cement product and method for manufacturing thereof wherein the glazed cement product can be obtained by applying a glaze onto the surface of a molded body of cement, burning the glazed body and hydrating the burned body to harden, and improved in the strength of a molded body of cement by using, for example, prestressed concrete steel.
Hitherto, there is employed a method of laying reinforcing steel within a glazed cement product in order to increase the strength thereof. The product can be obtained by the following steps.
At first, a kneaded mixture of cement comprizing cement, aggregate, water and the like is poured into a form wherein reinforcing steel is laid beforehand. Next, the resulting molded body of cement is hardened by curing in air for a prescribed time. Then the molded body of cement is applied a glaze onto the surface thereof, burned at a prescribed temperature and cooled in air. At the end, the burned molded body of cement is hydrated to harden for manufacturing a glazed cement product.
However, in case of manufacturing the above-mentioned conventional product, there is generated a thermal stress while burning and cooling are carried out between reinforcing steel and the portion of cement material caused by the difference of coefficient of thermal expansion between them, whereby cracks are generated within the portion of cement material. For example, the coefficient of thermal expansion of reinforcing steel is about 17.3.times.10.sup.-6.degree. C.sup.-1 and that of a molded body of cement is about 7 to 10.times.10.sup.-6.degree. C.sup.-1 which, of course, varies depending on the types of aggregate used or mixing ratio of cement, aggregate and water. Accordingly the reinforcing steel expands about twice as much as a molded body of cement. As a result, the conventional product has problems that the strength thereof decreases against expectation of increasing the strength thereof by reinforcing steel.
Accordingly, it is an object of the present invention to improve or remove the above-mentioned conventional drawbacks, and provide a glazed cement product wherein the generation of cracks is controlled and method for manufacturing thereof.